In the prior art, a toggle clamp disclosed in Japanese Laid-Open Utility Model Publication 63-136838 has been proposed. The toggle clamp of the above publication has a tightening force adjustment mechanism, which includes a base bracket, a workpiece pressing arm, and a handle. The workpiece pressing arm and the handle are designed to operate in cooperation via a toggle mechanism. The workpiece pressing arm is formed of a pair of strip-shaped arm plates to sandwich a vertical pin receiver of the base bracket. A slit is formed in each arm plate to extend in the longitudinal direction in parallel to the lower rim of the arm plate.
The slits receive the ends of a plate nut so that the plate nut slides freely. The plate nut includes rotation restricting steps, each of which is engaged with the rim of the corresponding slit. Furthermore, a U-shaped washer fitted to the lower rims of the arm plates has a central hole through which an adjustment bolt is inserted and screwed to the plate nut so that a lock nut on the adjustment bolt is tightened to the washer.
The tightening force adjustment mechanism of the toggle clamp adjusts the clamp position by moving the plate nut along the slits. However, since the adjustment bolt is fixed by the lock nut after adjusting the height of the adjustment bolt, the pressing force cannot be adjusted easily while clamping the workpiece.
That is, the height of the adjustment bolt needs to be adjusted by loosening the lock nut in a narrow space surrounded by the base bracket, the arm plates, and the workpiece. Thus, adjusting the pressing force applied to the workpiece is very troublesome.
Accordingly, it is an objective of the present invention to provide a clamping device that solves the problems of the prior art and finely and easily adjusts the pressing force while actually clamping a member that is to be clamped.